SQ-CARS: A Scalable Quantum Control and Readout System

• Published in: IEEE transactions on instrumentation and measurement Vol. 72; p. 1
• Main Authors: Singhal, Ujjawal, Kalipatnapu, Shantharam, Gautam, Pradeep Kumar, Majumder, Sourav, Pabbisetty, Vaibhav Venkata Lakshmi, Jandhyala, Srivatsava, Singh, Vibhor, Thakur, Chetan Singh
• Format: Journal Article
• Language: English
• Published: New York IEEE 2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Channels; Control systems; control-electronics; Electromagnetic pulses; FPGA; Frequency ranges; Interactive control; Interactive systems; Low pass filters; Microprocessors; Onboard data processing; quantum computing; Qubits (quantum computing); Read out systems; RFSoC; Room temperature; superconducting qubit; Superconductivity; Synchronism; Synthesis
• ISSN: 0018-9456; 1557-9662
• DOI: 10.1109/TIM.2023.3305656

Qubits are the basic building blocks of a quantum processor which require electromagnetic pulses in giga hertz frequency range and latency in nanoseconds for control and readout. In this paper, we address three main challenges associated with room temperature electronics used for controlling and measuring superconducting qubits: scalability, direct microwave synthesis, and a unified user interface. To tackle these challenges, we have developed SQ-CARS, a system based on the ZCU111 evaluation kit. SQ-CARS is designed to be scalable, configurable, and phase synchronized, providing multi-qubit control and readout capabilities. The system offers an interactive Python framework, making it user-friendly. Scalability to a larger number of qubits is achieved by deterministic synchronization of multiple channels. The system supports direct synthesis of arbitrary vector microwave pulses using the second-Nyquist zone technique, from 4 to 9 GHz. It also features on-board data processing like tunable low pass filters and configurable rotation blocks, enabling lock-in detection and low-latency active feedback for quantum experiments. All control and readout features are accessible through an on-board Python framework. To validate the performance of SQ-CARS, we conducted various time-domain measurements to characterize a superconducting transmon qubit. Our results were compared against traditional setups commonly used in similar experiments. With deterministic synchronisation of control and readout channels, and an open-source approach for programming, SQ-CARS paves the way for advanced experiments with superconducting qubits.